to be a by-product, which never comes until nature by itself has sought and found the means suitable to the animal's existence or constitution ; it is an aftermath comparable to the condition of animals thriving and plants in full bloom. And nature, they say, made no difference originally between plants and animals, for she regulates the life of plants too, in their case without impulse and sensation, just as also certain processes go on of a vegetative kind in us. But when in the case of animals impulse has been superadded, whereby they are enabled to go in quest of their proper aliment, for them, say the Stoics, Nature's rule is to follow the direction of impulse. But when reason by way of a more perfect leadership has been bestowed on the beings we call rational, for them life according to reason rightly becomes the natural life. For reason supervenes to shape impulse scientifically. This is why Zeno was the first (in his treatise On the Nature of Ma?i) to designate as the end " life in agreement with nature " (or living agreeably to nature), which is the same as a virtuous life, virtue being the goal towards which nature guides us. So too Cleanthes in his treatise On Pleasure, as also Posidonius, and Hecato in his work On Ends. Again, living virtuously is equivalent to living in accordance with experience of the actual course of nature, as Chrysippus says in the first book of his De finibus ; for our individual natures are parts of the nature of the whole universe. And this is why the end may be defined as life in accordance with nature, or, in other words, in accordance with our own human nature as well as that of the universe, a life in which we refrain from every action forbidden